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How To Determine Reagents In Organic Chemistry

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What Is A Reagent In Chemistry

Limiting Reactant Practice Problems
  • Ph.D., Biomedical Sciences, University of Tennessee at Knoxville
  • B.A., Physics and Mathematics, Hastings College

A reagent is a compound or mixture added to a system to cause a chemical reaction or test if a reaction occurs. A reagent may be used to find out whether or not a specific chemical substance is present by causing a reaction to occur with it.

Even Scarier Than A Synthesis By Itself Is The Following Exam Question/request:

Propose a reasonable mechanism to carry out the following synthesis.

This is where youre given one reactant, one product, and ONE or TWO sets of reagents.In other words, youre given all the steps but asked to show how the different molecules work together.

While the question is completely different, the concept is the same.

Well modify the initial questions slightly:

  • What functional group is present on the reactant?
  • What functional group is present on the product?
  • WHERE IS THE REACTIVITY ON THE STARTING MOLECULE? As in, where do I start the mechanism?
  • Which reactions do I know to convert from one to the other?
  • Do I know of a reaction that produces an intermediate to the above product?
  • A student recently showed me this exam question for which not a single student in his class got full credit.

    Let me preface this by saying YES, this is a tough question.BUT, if you think through it logically, youll realize that if you studied the individual steps and recognize them, you should be able to follow along.

    What If It Wasnt That Easy

    What if youre asked to start with an alkyne?

    We cant go from alkyne to alcohol directly, since the enol product would immediately tautomerize to a ketone or aldehyde.

    This is where we introduce many options:> If you reduce the alkyne to an alkene, you may use one of the following as already discussed above:

  • Acid catalyzed hydration of alkynes will yield a ketone following .
  • HOWEVER, in this example were starting with a 3-carbon chain yet ending with a 4-carbon chain.

    4. Do I know of a reaction that produces an intermediate to the above product?Yes! Terminal alkynes easily undergo chain elongation via SN2.

    We’ll start with an acid/base reaction to deprotonate the terminal alkyne forming a good nucleophile.

    We need to elongate the chain by just one carbon. Lets give this methyl group a good leaving group to facilitate a quick SN2 reaction my go-to is Bromine, but you can also use Chlorine or Iodine.

    Now that we have a carbon chain of desired length, lets carry out the acid catalyzed hydration.

    But wait, the product is an enol, not a ketone!!

    The next step will happen automatically. So while you dont have to show a reagent simply draw KET over the reaction arrow for Keto Enol Tautomerization.

    And there we have it!

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    The Secret To Synthesis Is Simple:

    A) Look for patterns, as well explain below.B) when you get stuck, remember theres likely more than one way to reach your desired product.

    Coming up with a proper synthesis requires a combination of forward and reverse thinking!

    Well cover the reverse thinking in the Retrosynthesis tutorial.For this tutorial, well focus on the shorter and simpler synthesis.

    Reaction Synthesis On Your Desktop

    Organic Chemistry Reagent Guide

    Reactor is a high performance, integrable reaction enumeration engine. It works with generic reaction equations that can be drawn in or defined and imported in various different formats, including among others: SMIRKS/SMARTS strings, RDF, RXN and MRV files. The Reactor package includes a large and continuously growing library of organic chemical reactions that can be utilized directly, without any further configuration.

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    Introductory Chapter: An Outline Of Chemical Reagents And Reactions In Inorganic Synthesis

    Submitted: October 18th, 2016Published: May 23rd, 2018

    DOI: 10.5772/intechopen.76536

    There are two ways to cite this chapter:

    There are two ways to cite this chapter:

    • Department of Chemistry, Urumu Dhanalakshmi College, India
  • Bhaskar Biswas*

  • Department of Chemistry, Surendranath College, India
  • *Address all correspondence to: icbbiswas@gmail.com

    Are Reagents Used In Coronavirus Test Kits

    Since mass testing has proven necessary to help flatten the curve of COVID-19 cases, laboratory tests are required to yield accurate results from screened samples. In order to ensure this, pre-approved reagent grade substances, compounds, enzymes, and other primers must be used for the specific analytical application of test samples. Doing this will ensure a verifiable set of data.

    Reagents used in coronavirus test kits are well-studied for safe and effective applications in biochemical tests, specifically towards an accurate detection of certain virus strains via RT-PCR-based screening. In rapid antibody tests, the reagent used is actually the patientâs blood, which is used to detect COVID-19 antibodies.

    Above anything else, chemical reagents are indispensable requirements of coronavirus tests. Without them, we would just be left with inaccurate, epidemiological guesses.

    Disclaimer

    All content published on the ReAgent.co.uk blog is for information only. The blog, its authors, and affiliates cannot be held responsible for any accident, injury or damage caused in part or directly from using the information provided. Additionally, we do not recommend using any chemical without reading the Material Safety Data Sheet , which can be obtained from the manufacturer. You should also follow any safety advice and precautions listed on the product label. If you have health and safety related questions, visit HSE.gov.uk.

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    Mcat Organic Chemistry Tip #: Understand Experimental Techniques Commonly Used In Organic Chemistry Such As Separations Purifications And Spectroscopy

    The MCAT will expect you to be familiar with these basic organic chemistry tools, and we will walk through the details you need to know of each technique in our Ch. 5 guide on spectroscopy, separations, and purifications. Here, however, is a good place to remind you that anytime you miss an MCAT organic chemistry question while doing practice, be sure to go back and review that question, write down what you needed to know to get the question right, and study that new information. You shouldnt just do this for practice organic chemistry questions, you should do it for all practice questions that you take.

    How Do You Choose A Solvent For An Organic Reaction

    Organic Chemistry Reactions Summary

    For the specific reaction you mention, here are some criteria you would consider to select a solvent: Because this is an oxidation reaction, choose a solvent that cannot be oxidized, known as an aprotic solvent. The solvent needs to dissolve the reagents in the reaction: hypochlorite and 4-tert-butylcyclohexanol.

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    What Is A Tollens Reagent Test

    Named after its German chemist discoverer, Bernhard Tollens, the Tollensâ reagent test is used to identify aldehydes and their functional groups, as well as to distinguish between these and ketones.

    Central to this test is the Tollensâ reagent, which is composed of ammonia and silver nitrate, as well as sodium hydroxide, in order to stabilise the pH level of the reagent solution. A positive result using this test is determined when a precipitated âsilver mirror effectâ is produced on the surface of the reaction vessel, demonstrating that the reagent has been utilised. Meanwhile, the presence of ketones would yield a negative result, except in the case of alpha-hydroxy ketones.

    The short shelf life of the Tollens reagent means that a fresh laboratory preparation must be made prior to its immediate usage. There are three main applications that this reagent is used in:

    • Quantitative organic analysis, where the Tollens reagent is used to differentiate between aldehydes and ketones
    • Anatomic pathology, where itâs used to detect chromaffins, melanin, argentaffin, and lipofuscin in histology
    • Material science, where itâs used to apply a high-quality silver mirror on glass surfaces of commercial products, including scientific apparatus

    Mcat Organic Chemistry Practice Questions

    1. A researcher performs an organic reaction in which a benzene with an alcohol substituent turns into a benzene with an aldehyde substituent. Which of the following peaks may appear for the product in IR spectroscopy?

    A) Broad, 3500 cm-1

    2. Which of the following best describes why protic solvents decrease nucleophilicity?

    A) Protic solvents are too sterically bulky and prevent the nucleophile from contacting the electrophile.

    B) Protic solvents alter the chemical properties of the electrophile to decrease the reaction efficiency.

    C) Protic solvents can hydrogen bond with the nucleophile, thereby decreasing the frequency of nucleophilic attack.

    D) Protic solvents introduce a net positive charge to the nucleophile and decrease nucleophilicity.

    3. A researcher is studying a molecule with three chiral centers. The researcher obtains a racemic mixture after several steps of purification. Which of the following stereochemical designations could the researcher have obtained?

    A) S,S,S and R,S,R

    D) Carboxylic acid

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    E1 And E2 Reactions In The Laboratory

    E2 elimination reactions in the laboratory are carried out with relatively strong bases, such as alkoxides . 2-Bromopropane will react with ethoxide, for example, to give propene.

    Propene is not the only product of this reaction, however the ethoxide will also to some extent act as a nucleophile in an SN2 reaction.

    Chemists carrying out laboratory nucleophilic substitution or elimination reactions always have to be aware of the competition between the two mechanisms, because bases can also be nucleophiles, and vice-versa. However, a chemist can tip the scales in one direction or another by carefully choosing reagents. Primary carbon electrophiles like 1-bromopropane, for example, are much more likely to undergo substitution than elimination this is because the electrophilic carbon is unhindered and a good target for a nucleophile.

    SN1 and E1 mechanisms are unlikely with such compounds because of the relative instability of primary carbocations.

    The nature of the electron-rich species is also critical. Acetate, for example, is a weak base but a reasonably good nucleophile, and will react with 2-bromopropane mainly as a nucleophile.

    Also, a strong hindered base such as tert-butoxide can be used. The bulkiness of tert-butoxide makes it difficult for the oxygen to reach the carbon . It is more likely to pluck off a proton, which is much more accessible than the electrophilic carbon).

    About Iodine Reagent Tests

    Identify the reagents that you would use to synthesize each of the ...

    Yellow or brown iodine solutions are commonly used to detect starch. If starch is present, iodine turns blue or black in colour, and this method can be used to distinguish glucose and carbohydrates from starch. Unlike Benedictâs reagent, iodine reagents react strongly with starches, making them more suitable for this application.

    Which Reagent Is Used To Test For Starch?

    Starch has neither odour nor taste. Itâs a white substance in its pure form, and can be found in plant tissues, although itâs commonly obtained from cereals and potatoes. Starch is also called amylum, which is a polymeric carbohydrate composed of various units of glucose. Itâs technically a polysaccharide, or a complex sugar used as food or energy storage by plants.

    Iodine solution is used as a reagent to test for starch because its sensitivity means that it can differentiate starch from glucose and other carbohydrates. If you want to see this reagent in action, put some iodine on a potato and watch as it turns black!

    Which Reagent Is Used To Test For Alkenes?

    Alkenes are double-bonded hydrocarbons used for alcohols, plastics, detergents, and fuels. Bromine water is the reagent of choice when it comes to testing for alkenes.

    C2H4 + Br2 â C2H4Br2

    Non-dibromo products can also be produced with this reagent. For example, if distilled vapour or steam is incorporated with an alkene, an alcohol is produced for instance, when ethene and water form ethanol:

    C2H4 + H2O â C2H5OH

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    Get Synthesizable Molecules By Proper Reaction Rules

    The reaction rules are defined in Chemical Terms, Chemaxons scripting language that is designed to add chemical intelligence to cheminformatics applications. Through Chemical Terms a large number of calculated properties can be included in the reaction rules to produce valid compound libraries. Besides calculating physicochemical properties on-the-fly, the Chemical Terms language also supports importing arbitrary fields from the input reactant files used in the evaluation of the reaction rules.

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    Lets Start By Looking For Patterns

    The following questions will help you understand what to pay close attention to.

    Look out for the following:

  • What functional group is present on the reactant?
  • What functional group is present on the product?
  • Which reactions do I know to convert from one to the other?
  • Do I know of a reaction that produces an intermediate to the above product?
  • For example:If you’re starting out with a 4-carbon alkene and the product asks for a 4-carbon alcohol, ask yourself,

    What do I have in the reactant?A reactive pi bond!

    What do I have in the product?An alcohol.

    Which reaction do I know can help me convert from an alkene to an alcohol?

    Well, there are many if you think about it. Lets go in order from most obvious to less obvious:

    • Acid catalyzed hydration
    • Oxymercuration-demercuration
    • Hydroboration-oxidation

    These are the direct obvious reactions with potentially differing results. We’ll use 3-methyl-1-butene to highlight these difference.

    But what if you werent given the alkene, or didnt think of these alkene reactions?What about putting a halogen leaving group on the alkene through hydrohalogenation?Or a radical halogenation if starting with an alkane?

    Then you can carry out an SN2 reaction using NaOH in a polar protic solvent.

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    Different Types Of Chemical Reagents And Their Uses

    Lucy Bell-Young

    In chemistry, reagents are compounds, substances, or mixtures used to examine chemical reactions. Commonly, a reagent is incorporated into a test to either produce a chemical reaction, or to check if a reaction would occur to begin with. Read on to discover more about how chemical reagents work, and what role theyâre playing in coronavirus test kits.

    In this post:

    What Is A Benedicts Reagent Test

    Grignard Reagent Reaction Mechanism

    American chemist Stanley Rossiter Benedict is the namesake behind Benedictâs reagent test. This involves a complex chemical reagent composed of copper sulfate pentahydrate, sodium citrate, and sodium carbonate.

    The test is often used to detect reducing substances, like sugars, by checking for a colour transition from blue to red-brown, with a precipitate:

    • To test for the presence of monosaccharides or reducing disaccharides in certain ingredients, a sample is first dissolved in water
    • A certain amount of Benedictâs reagent is then added to the solution, and the resulting colour is what will determine the results

    Like the Tollensâ reagent test, the Benedict reagent test can detect the presence or absence of aldehydes and alpha-hydroxy ketones, as well as hemiacetals . It can also be used to identify high amounts of glucose present in urine, which could be indicative of something like diabetes mellitus. However, this test isnât the main method used for glucose analysis, since its high sensitivity can lead to false positives.

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    Answer Key For Mcat Organic Chemistry Practice Questions

    1. Answer choice D is correct. In the product, a carbonyl group is forming , and this is seen on an IR spec at 1700 cm-1 as a sharp peak . A broad peak around 3500 cm-1 is characteristic of an OH, which we would see for the reactant, not the product .

    2. Answer choice C is correct. By forming hydrogen bonds with protic solvents, nucleophiles cannot move as freely in solution and it is harder for them to attack electrophiles . Protic solvents are not necessarily sterically bulky water is an example of a protic solvent . The question asks how protic solvents affect then nucleophile, not the electrophile . While protic solvents might make the nucleophile less negative, they are highly unlikely to introduce a positive charge to the nucleophile .

    3. Answer choice B is correct. A racemic mixture occurs when an enantiomer pair is present in equal amounts. Enantiomers have opposite stereochemistry at every chiral center .

    4. Answer choice A is correct. Charge, electronegativity, H-bonding capacity, and steric bulk are important in determining how strong a nucleophile is. Here, hydroxide ions are negatively charged , strongly electronegative, and have no steric hindrance . Water and ethanol are not very strong nucleophiles . Tert-butanol has a lot of steric hindrance .

    Brief On Reagents In Organic Chemistry:

    Chemical reactions seem to get triggered when reagents are utilised. Reagent organic compounds seem to react and cause a chain reaction in various parts of the body some inorganic substances are also included in the reagent category as they are used to trigger reactions manually. The interaction of reagents when used with another compound or multiple other related compounds cause specific reactions, which are widely utilised in testing for any presence of specific substances.

    The phrases reagent, as well as a reactant, seems to get occasionally used in a similar way, but they are not the same thing. A reagent seems to bind itself to a compound when used within a chemical process, resulting in the triggering of a chemical reaction. When this process happens, the reagent doesnt get absorbed, but a reactant seems to get absorbed in the process. This is why the reagents are referred to or categorised under the catalyst section, unlike reactants.

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    Is Organic Chemistry Just Memorization

    The number one reason people find organic difficult is they try to memorize everything. This course is not about memorization. You cant memorize hundreds of reactions, and you certainly cant memorize Stereochemistry. Treat organic like a math course work lots of problems and learn the process.

    Create And Test Your Reactions

    Solved Provide the reagents needed for the following

    Reactor has an integrated reaction sketcher and editor tool. Users can create their own reaction schemes and add corresponding reaction rules by using the Chemical Terms language. The created reaction schemes can be easily tested and the reaction rules can be validated using the integrated reaction testing tool in Reactor.

    Knowledge Hub

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    Is Organic Chemistry Easy

    If you know the chemistry them, you can characterize most reactions just by your own knowledge, with little memorization at all. Organic chemistry is not as difficult as its reputation makes it out to be. I enjoyed the course and personally found it to be significantly easier than general chemistry.

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